The present invention relates to the field of firearms, more particularly it is an improvement of the constructive technique of any type of firearms, like for example semiautomatic and non semiautomatic hunting rifles, military assault guns, machine guns, gunnery in general, as well as shotguns, so as to allow the employment of different types of ammunitions in absolutely safe conditions.
According to the present invention, a device is provided which allows the user to increase or decrease as it suits him and according to the needs of the specific moment, the initial values of the pressure generated by the travelling charge (powder), following its ignition.
Since the pressure that builds up during gunpowder combustion is directly accountable for the speed which is given to the projectile, it is possible to adjust its speed and ensuing kinetic energy, and in so doing varying the amount of energy given up to the target which is located at a certain distance.
In such a way it is advantageously possible to study new types of ammunitions (new calibers with particular amounts of propellent) with the aim of attaining a better quality from both the ballistics and the construction points of view.
It is known, from U.S. Pat. No. 3,381,403, a projecting unit for projecting a syringe projectile for administering of drugs, medicines and the like to animals.
This known apparatus is externally similar to a firearm such as a rifle or a pistol, but it is specifically designed to fire only explosive ballistic cartridge blank in order to provide propulsive power to a syringe projectile by means of a pre-expansion chamber.
The arrangement disclosed in U.S. Pat. No. 3,381,403 does not allow the use of different kind of ammunitions with the same firearm, but instead is only intended for the use of syringe projectiles having different weight with a same kind of blank cartridge.
It is also known, from ER 491.222, a device suitable for reducing the range of a gun or cannon (without varying the inclination of the barrel) by discharging a desired amount of the combustion gases, produced by the gunpowder combustion contained in the ammunitions, in the external environment. For this aim, FR 491.222 discloses a gun having a combustion gas discharging conduit that may be closed or opened by the user.
In this latter case, the discharged combustion gases are lost and they are not re-utilized for propelling the projectile.
The firearms known in the art were conceived and designed to endure and operate with explosive charges of a certain intensity, therefore the pressure that is generated in employing ammunitions with the same caliber but with bigger charges is very dangerous, as much higher pressure values are reached when compared with those that are expected at the designing stage The xe2x80x9clivelinessxe2x80x9d of the powder and the limited volume available to combustion gases when they expand, a volume which is made available by the initial headway motion of the projectile, are concurring factors when pressure builds up to unacceptable values.
In these conditions, both the case and the weapon are mechanically strained, whereas the bullet receives a xe2x80x9cram blowxe2x80x9d, which negatively affects its precision on the target.
Besides that, the mobile recoiling parts respond in such a way as to be factors that greatly increase the possibilities that structural failures occur in whatever weapon, with consequences that can be easily guessed, especially in machine-gun-type weapons, like said machine guns and military assault shotguns with a shooting range beyond 550-650 shots per minute.
It is well known that gunpowder has two important inherent features, the first being that the oxygen which is necessary for combustion to take place is intimately contained within the chemical formula of the gunpowder itself, therefore this can burn in the absence of air, that is in an airtight environment (case), whereas the second feature which is ever more important, is that the rate at which said combustion occurs is proportional to the pressure itself.
In other words, when the percussion has been triggered and it gives way to the beginning of the combustion of the charge contained in a case, the gas which is given off yields to a pressure increase around that charge which still has to burn. At this point the fundamental phenomenon because of which the powder reacts to yield a blast from being a simple combustion takes place.
This sudden pressure increase strongly accelerates combustion, with an ensuing production of further gas and a pressure increase, therefore a higher combustion rate.
Such a process is so fast that it seems to be instantaneous.
To understand the importance of the phenomena which have been described so far, it is enough to point out that an amount of gunpowder that only needs a couple of seconds to burn in the open air is consumed within a couple of thousandths of a second when it is compelled in a case.
Although very rapid, the combustion process described so far is the result of a sequence of events that can be controlled.
From the moment when the initiator lights the charge of a cartridge which is located in the chamber, the pressure starts to undergo a rapid increase, and the only xe2x80x9cyieldingxe2x80x9d point within the blasting volume inside the case is the projectile, therefore compressed gases exert their propulsive action forcing the projectile out of the neck of the case and accelerating it along the muzzle (where the word xe2x80x9cmuzzlexe2x80x9d is to be understood to include the entire barrel from the front end of the cartridge chamber to the exit of the barrel).
Within this very limited time lapse, the best possible ratio must be attained between the rate of production of the gases that are given off by charge combustion and the rate at which the volume that they occupy increases when they expand.
It is essential to point out that the above volume is that given by the space between the bottom of the case and the base of the projectile. Therefore it linearly augments as the latter moves forward along the muzzle.
Therefore it is clear that the above ratio is extremely important and delicate.
If the charge burns too rapidly when combustion has just begun and the projectile has only travelled a short way along the muzzle, too much gas is produced and there is not enough space for its expansion to occur; this leads to an increase in pressure up to extremely high values that may even burst the breech of the gun.
From the safety point of view, the maximum pressure value is a very useful datum for an appraisal of how close a certain type of ammunition is to its failure limits or to those of a specific weapon.
Nowadays, the employment of heavy ammunitions leads bullets to have higher initial speeds, tauter trajectories and greater kinetic energies, which means greater energies that can be given up, and increased penetration power.
One of the greatest problems of the prior art is given by the fact that free burst functioning with these heavy ammunitions would lead the weapon to undergo structural failures because of the excessive volume of gases produced during the explosion of the projectiles charges.
Gas recovery systems are known in the art, but their only aim is that of expelling the exploded case so as to maintain the automatism in the functioning cycle of the weapon itself.
Since when smokeless gunpowder was discovered, that is more than a century ago, ammunition propellents have been manufactured thanks to techniques which developed with the objective of controlling combustion rate.
Therefore it necessary to find a way to slow down the propellent combustion rate, accomplishing both a decrease in the initial pressure and a saving of part of the charge which is bound to burn later, consequently warranting a pressure which is suitable to the volume generated by the headway movement of the bullet along the muzzle.
An object of the present invention is that of increasing the volume made available to combustion gases following their expansion, by providing an expansion chamber whose volume can be adjusted.
In other words, according to the present invention, it is possible to adapt the physical features of the gun to the type of ammunition that is to be employed.
According to the invention, there is given a firearm which is equipped with a device, apt to adjust shot initial pressures, by dint of an ad hoc device which is calibrated to the millimeter range.
Such an adjustment device has a simple and rational shape, and it can be envisaged as substantially comprising three mechanical elements; an expansion chamber that communicates with the firearm muzzle through at least one connection hole, moreover a front and a back adjustment screws.